1. Field of Invention
The invention is a pickup head actuator for carrying a plurality of near- or far-field optical or magnetic I/O elements. In particular, the invention pertains to a pickup head actuator that is able to provide different working heights.
2. Related Art
Magnetic recording and optical recording have been widely used for data storage. Common magnetic recording media include floppy disks and hard drives, all of which have magnetic heads flying at a distance less than 1 μm from the disks. Well-known optical recording media include CD's (Compact Disc), DVD's (Digital Versatile Disc), and MO's (Magneto-optical Disc). The storage methods of these optical recording media utilize an objective lens with a specific NA (Numerical Aperture) to focus a laser beam on the discs. The distance from the objective lens to the disc (the so-called working height) is usually far larger than the wavelength of the laser beam. Therefore, they are called far-field optical recording media.
With the advance in modern technologies, to achieve storage of higher-density data a lot of near field optical data recording have appeared. Such devices as the SIL (Solid Immersion Lens), the SIM (Solid Immersion Mirror), and the VCSEL (Vertical Cavity Surface Emitting Laser) use a flying head to perform data recording at a height within 100 nm.
Although near field optical recording can greatly increase the data storage density, it is nevertheless incompatible with far field optical recorders. This results in extra costs for consumers. Moreover, even far field recording elements differ in their focal lengths. Therefore, it is of urgent needs to provide a pickup head compatible with all sorts of far field optical recording media, the near field optical recording media, and even magnetic recording media.
To solve the compatibility problem, there were many methods proposed in the prior art. For example, the U.S. Pat. No. 5,864,524 provided a structure of a base installed with two objective lenses. The base can be rotated under the interaction of a side magnet and a coil on the base, selecting one of the objective lenses to work. With reference to FIG. 1, the base 12 has a first objective lens 121 and a second objective lens 122. The work heights of the objective lenses 121, 122 are different and the base 12 only rotates horizontally relative to the disc 11 to select an appropriate work objective lens. When the second objective lens 122 with a lower work height is used, data access can be properly performed. When the first objective lens 121 is used, the disc 11 has severe vibrations because the storage media with a larger work height has a lower precision. This does not have much influence on the first objective lens 121, but may cause damages to the closer second objective lens 122. The result of such severe vibrations can possibly erode the second objective lens or have scrapes and cuts on the disc 11. This obviously is a big disadvantage of composite-lens pickup heads. Thus, the applications are only good for far field recording media with different focal lengths, e.g. CD-DVD systems.